Field of the Invention
The present invention relates to an image forming apparatus including an optical sensor for receiving, by a light receiving element, reflected light of light emitted from a light emitting element to detect a detection target.
Description of the Related Art
In recent years, in electrophotographic image forming apparatuses, a tandem type which is a configuration in which a photosensitive member is arranged for each color to accelerate printing speed has become mainstream. In a tandem type image forming apparatus, a color misregistration amount is determined by forming a detection image (a toner image) which is a test pattern for detecting a color misregistration amount on an intermediate transfer belt, for example, and then irradiating light onto the detection image and detecting light reflected therefrom by an optical sensor. Also, a determination of a density of a toner (a density of an image) using such an optical sensor has been performed. In Japanese Patent Laid-Open No. H10-221902, a technique is disclosed in which a diffused reflection light and a specular reflection light of light irradiated on a toner image are respectively received by individual light receiving units (sensors), and based on the received light amounts, the density of toner is detected. By virtue of such a technique, it is possible to improve precision of detection of toner by an optical sensor even if toner of a plurality of colors used in the image forming apparatus has reflection characteristics that differ with respect to the light used by the optical sensor.
In an optical sensor of the foregoing type, generally, in addition to providing an aperture for limiting (narrowing) light that the light emitting element emits, that kind of aperture is also provided for the light receiving elements that respectively receive specular reflection light and diffused reflection light in order to separate the specular reflection light and the diffused reflection light. Surface-mounted type optical sensors in which an optical element is mounted directly on a surface of a circuit board are disclosed as such kind of optical sensors in Japanese Patent Laid-Open No. 2006-208266 and in Japanese Patent Laid-Open No. 2013-191835.
In Japanese Patent Laid-Open No. 2006-208266, an optical unit holder is attached to a circuit board on which a light emitting element and two light receiving elements are directly mounted, and three polarization filters respectively corresponding to the light emitting element and the two light receiving elements are arranged on an outside surface of the optical unit holder. However, when a plurality of polarization filters are used in this way, it leads to an increase in apparatus cost, and a reduction in productivity. Meanwhile, in Japanese Patent Laid-Open No. 2013-191835, a housing having an opening (a light guiding path) that functions as an aperture corresponding to each optical element (the light emitting element and the two light receiving elements) is configured such that light shielding walls that configure the openings are inserted in a slit hole arranged in a circuit board. This improves a light-shielding property in an optical sensor configured by mounting each optical element on a surface of the circuit board.
However, in the optical sensor described in Japanese Patent Laid-Open No. 2013-191835, it is necessary to arrange the light emitting element and the two light receiving elements at a certain distance from each other in order to realize the housing that improves the light-shielding property. Even if it is possible to improve the light-shielding property by virtue of this kind of optical sensor configuration, the size of the optical sensor is larger in a direction in which the light emitting element and the two light receiving elements are arranged. Accordingly, it would be desirable to realize further miniaturization in the optical sensor.
Depending on a configuration for realizing miniaturization of the optical sensor, cases may occur in which the light-shielding property between the light emitting element and the light receiving elements cannot be sufficiently ensured due to a reflection of light that arises within the housing of the optical sensor. If reflected light that arises within the housing of the optical sensor is irradiated onto the light receiving element, an error that depends on a received light amount of such reflected light will occur in the detection result of the received light amounts by the light receiving elements.